1. Field of the Invention
This invention is directed to an exothermic, controlled flow solution polymerization system and process. In particular, this invention pertains to a non-adiabatic, substantially well-mixed solution polymerization system and process for making ethylene, propylene, and styrene polymers including, but not limited to, polypropylene, styrene block copolymers, ethylene-propylene-diene monomer (EPDM) elastomers, ethylene-propylene (EP) elastomers, ethylene-styrene copolymers, ethylene/alpha-olefin interpolymers, and polyethylene.
2. Description of Related Art
Olefin manufacturers have long sought the ability to offer a wide range of product types all produced from a single process platform. With the development and advancement of metallocene catalyst complexes and the continued advancement of traditional Ziegler coordination catalyst systems, the potential has emerged to manufacture diverse olefin polymer types using a single polymerization system. With the recognized polymer product advantages derived from solution polymerization systems (relative to gas phase and slurry or particle-form processes), well-mixed, single- phase solution polymerization has been long perceived as the candidate process to allow full exploitation of various olefin catalyst advancements. However, known solution polymerization systems (i.e., adiabatic stirred tank reactor processes) have important shortcomings that must be resolved before the desired catalyst/polymer product exploitation can be realized. That is, significant process advancements are required beyond adiabatic, stirred reactor solution polymerization. For example, as a primary requirement, the desired solution polymerization system should accommodate or efficiently utilize the wide range of exothermic heats of reaction (heat of polymerization) occurring with respect to various olefin polymer types; for, example, ethylene polymerization being a relatively high heat generator and styrene polymerization being a relatively low heat generator.
Also, to meet accelerating volume potentials for olefin polymers manufactured using various catalyst advancements, particularly advancements pertaining to metallocene catalyst complexes, the desired solution polymerization system should accommodate or utilize the wide range of heats of reaction while maintaining high polymer production rates. Moreover, high productivity should be accomplished without the so-desired solution polymerization system being cost prohibitive to construct or operate, nor excessively large in physical size.
In particular, the desired solution polymerization system should overcome the typical limitations of adiabatic polymerizations wherein polymer concentration and conversion can not be adjusted freely and/or independently. That is, if the heat of reaction or polymerization can be removed from the polymerization system by means external to the polymerization reaction, then polymerization conditions, such as reactor temperature and polymer concentration, could be selectively controlled to selectively optimize polymer production rates, polymer structure, and catalyst efficiencies.
Himont's Spheripol process is well-known in the art of olefin polymerization. Loop polymerization systems are well-known for manufacturing polystyrene.
Meyer discloses in a paper presented at the AIChe Annual Meeting, Los Angeles, Nov. 17-22, 1991, the heat transfer capacities per unit volume for various reactor types. In FIG. 9 of the paper, Meyer discloses that pipe adapted with static mixing devices offers only incrementally improved heat removal relative to empty pipe or a stirred tank reactor. This same figure was also published as FIG. 11 in Chemical Plant & Processing, November 1989, the disclosure of which is incorporated herein by reference. The figure discloses that a static mixer/heat exchanger apparatus comprised of tortuous tubes or conduit pipes is a substantially superior heat exchange apparatus at process volumes greater than 1 cubic meter.
While various polymerization systems and/or reactor types are known for making various products, no known polymerization system or process meets the above stated object. That is, conventional, known loop reactor technology (such as, for example, standard engineering design packages commercially available from Koch which can also include known static mixer/heat exchanger reactors) do not meet the above stated object. For example, while known loop reactor technology can be readily employed for olefin polymerizations characterized by relatively low process side volumetric heat removal requirements, experiments show such technology is ill-suited for olefin polymerizations requiring relatively high heat removal rates.
For olefin polymerizations requiring high heat removal rates, known loop reactor systems are generally restricted to large process volume/size requirements, high recycle ratios and/or low production rates. Also, at least when used for high heat removal/high productivity solution polymerizations, known loop reactor systems are characterized by poor feed/catalyst mixing which results in the occurrence of cold, monomer-rich regions in the reactor system. The occurrence of these regions invariably results in the preparation of polymer product with undesirable polymer fraction, such as, for example, polymer fractions having a higher molecular weight and/or higher density relative to the bulk polymer. Also, these cold, monomer-rich reactor regions can give rise to liquid and/or solid separation (i.e., maldistribution) which in turn results in reactor instability, fouling, and plugging as well as gel formation and product compositional heterogeneity.